Data reproduction process



United States Patent 3,309,243 8 DATA REPRODUCTEUN PIRQCESS Elliot Herman, Braintree, and Hollis E. French, Woburn, Mass assignors to ltek Corporation, Lexington, Mesa, a corporation of Deiaware No Drawing. Filed June 3, 1963, Ser. No. 234,303 13 Claims. (Cl. 96-49) This invention relates to data reproduction processes and relates particularly to data reproduction processes employing improved heatand light-sensitive compositions comprising a diazosulfonate salt and a coupling agent. The invention also relates to such improved heatand light-sensitive compositions and to their use in data reproduction processes.

Heatand light-sensitive compositions containing aryl diazosulfonate salts and coupling agents are known in the art, and have been used in processes for data reproduction. Such processes make use of the following reactions to reproduce data, such as graphic or pictorial images:

heat diazo compound coupler azo dyestulf llight decomposition with liberation ol nitrogen A typical conventional diazotype reproduction process involves the sensitization of a base or carrier, such as paper, with a composition containing a light-sensitive diazo compound such as a diazonium salt. The sensitized base is then exposed to light under an image pattern. Where light strikes the sensitized base, the diazonium compound is decomposed or burnt out in the areas exposed to light. A colored image is then developed in the areas not exposed to light by reaction of the remaining diazonium compound in the unexposed areas with a coupler to give an azo dye. Conventionally the coupler is included with the diazo compound in the sensitizing coating and the coupling reaction is simply effected by heating.

In working with prior art systems of this type, the applicants have observed that aryl diazosulfonate salts behave anomalously. As the light sensitivity of such a heatand light-sensitive system is increased, due to the choice of particular highly light-sensitive aryl diazosulfonate salts employed, the thermal sensitivity of the system decreases. This experience runs contrary to what would be expected by those skilled in the art, since sensitivity to heat and light are both ultimately dependcut on the molecular structure of the diazosulfonate salts employed and both would normally be expected to decrease and/or increase as diazo compounds with greater or lesser molecular stability were investigated.

The applicants believe that this anomalous behavior of aryl diazosulfonate salts may be due to the existence, in a system containing such salts, of the following equilibrium:

That is, in the system, the diazosulfonate salts (where R above is an aromatic radical and X is a metal ion, such as an alkali metal ion) are in equilibrium with 21 diazonium cation and a metal sulfite anion.

The applicants have found that some diazosulfonate salts RN=NSO X per se are not light sensitive. This has been shown by flashing these compounds in mineral oil without effecting their decomposition. That is, under conditions suppessing the equilibrium shown above, there is little or no decomposition of the diazosulfo-nate salt in the presence of light: the light-sensitive species is the diazonium cation in equilibrium with the diazosulfonate compound.

Further, the applicants have found that the diazonium cation RNEN+ will not react significantly with a coupler in the presence of heat since the rate of thermal decomposition of the cation is faster than its rate of coupling: the heat-sensitive species in the coupling reaction is probably the diazosulfonate salt.

The applicants have discovered that diazotype systems employing arromatic diazosulfonates salts and a coupling agent can be modified in a manner permitting the use of diazosulfonate salts having increased light sensitivity without incurring the concomitant loss in heat sensitivity which has heretofore been observed in the prior art when such highly light-sensitive materials have been used. This result is achieved by adding a dissociable diazonium salt to systems containing an aromatic diazosulfonate. The presence of the dissociable diazonium salt (i.e. the presence of diazonium cations) suppresses the ionization of the diazosultonate according .to the equilibrium shown above and thus increases the concentration of the thermally sensitive diazosulfonate salt in the system.

Nevertheless, such a system retains high light-sensitivity because under the influence of light the diazonium cation added to the system as a diazonium salt readily decomposes, permitting ionization of the heat-sensitive diazosulfonate salt to form still more of the decomposable light-sensitive diazonium cation.

In addition, the applications have discovered that when ortho-substituted dihydroxy couplers are employed in a system of the type just described, the presence of borax in the composition inhibits coupling reactions at room temperature and/or under highly humid conditions, thus advantageously stabilizing the composition.

Numerous diazosulfon-ate salts suitable for use in the compositions of the invention are well known in the prior art. Materials of this type are shown in US. Patents 2,217,189, 2,694,009, 2,974,042, 2,995,442, 2,994,608, and 3,029,146, for example. Particularly good results have been obtained in the present invention when using alkali metal p-amino diazosulfonates having nuclear alkyl or allcoxy substitutents and having one or more N-substituents discouraging air oxidation of the amino group. These N-substituents may be monoor di-alkyl groups, for example, or the nitrogen atom may be included in a ring system such as a morpholino group.

As couplers in the system of the invention, the socalled active couplers also conventional in diazo systems such as phloroglucinol, resorcinol, 8-naphthol, etc. can be used. A coupler particularly preferred according to the present invention is 2,3-dihydroxynaphthalene, both because of the colors of the azo dyes formed with this coupler and because of the ease with which the material couples to form such azo dyes.

The systems of the invention additionally critically contain a diazonium cation preferably, but not necessarily, corresponding with the diazo nucleus of the diazosulfonate materials employed. For example, when the preferred material 2-methyl-4-diethylaminobenzene diazo sodium sulfonate is used in combination with a coupler, the system also critically contains added quantities of a diazonium ion such as Z-rnethyl-4-diethylaminobenzene diazonium ion, suitably present as a salt, conveniently a halide salt, such as the diazonium chloride, bromide, or iodide. Any amount of dissociable salt added to the diazosulfonate will disturb the equilibrium shown earlier and increase the concentration of heat-sensitive diazosulfonate in the system to a value above its equilibrium concentration in the absence of added diazonium cation at comparable conditions of temperature and solvation. However, the addition of excessively large amounts of diazonium cation will only increase the time for bleaching a system containing these ions under light without contributing to color formation since, as noted earlier, the diazonium ion does not participate significantly in thermally induced coupling reactions in view of its more rapid thermal descomposition in a competitive reaction. For those systems comprising a coupler, a diazosulfonate salt, and a diazonium cation which are of practical interest in commercial data reproduction processes, the ratio of added diazonium salt to diazosulfonate salt present in the system may vary from 1:4 to 1:8. Nevertheless, it should specifically be noted that the basic inventive principle of suppression of the equilibrium ionization of the diazosulfonate salt is operative when even the smallest amount of diazonium cation is added to the system (since the additional presence of the cation will upset the equilibrium when present in even small amounts) and is equally applicable when extremely large amounts of the diazonium cation are added to the system.

The systems of the present invention are conveniently employed in data reproduction processes by coating them in layer form onto a suitable carrier or substrate material such as of wood, glass, plastic, fabric, paper, or the like. Usually the materials are used to produce coated papers for data copying or reproduction processes. Such coated substrates, particularly coated papers, are useful in a number of reproduction processes including the so-called reflex process and the so-called heat developable diazo process.

In the reflex process, the copy sheet containing the heat and light sensitive diazo layer is placed coated face up atop and in contact with the original to be reproduced. For this process a material transparent to infrared radiation, such as the infrared transparent papers known to the art, is used as the carrier for the diazo coating. The copy and original are then exposed to infrared radiation, such as a source of radiation in the near infrared, through the copy sheet. In those portions of the original in which there is an image, such as typewritten characters, the image area absorbs and retains the infrared light passing through the transparent copy sheet, whereas the nonimage bearing areas of the original absorb heat less strongly. In the image bearing areas of the original, where heating develops, the heat is transferred back to the heat-sensitive layer of the copy sheet in contact with the original. In these areas, coupling between the (hazesulfonate and coupler occurs to reproduce the original image. The resulting copy is subsequently fixed by exposing the copy sheet to ultraviolet light which bleaches those areas where no coupling reaction has occurred by destroying the photosensitive diazoniurn cation in equilibrium with the diazosulfonate salts present in the heatand light-sensitive layer of the copy sheet.

In the heat developable diazo process, a substrate material coated with the heatand light-sensitive compositions of the invention is exposed to an ultraviolet source through the original to be copied, which latter must be transparent to ultraviolet light. Ultraviolet light pass ing through the non-image areas of the original will destroy the diazosulfonate material in the sensitive layer of the underlying copy sheet by photo-destruction of the diazonium ion in equilibrium with the diazosulfonate salt. Where the ultraviolet light is blocked by image areas in the original and does not reach the copy sheet, the diazo layer of the copy sheet will remain unchanged. After exposure to an ultraviolet source as described above, the copy sheet may then be heated to cause coupling of the diazosulfonate salts and coupled remaining in the copy sheet under the image areas of the original to form a colored copy of the original image.

Thus, while the reflex system requires a substrate material for the heatand light-sensitive coatings of the present invention that is transparent to infrared, the heat developable diazo process may employ a copy sheet of any suitable material, but can only be used with originals which are transparent to ultraviolet. The coating of infrared transparent substrate materials with the heatand light-sensitive coatings of the invention adapts the sensitized substrate to use in either process. Infrared transparent materials suitable for use as carriers or sub strates for the sensitive compositions of the invention are known in the art, and includes, for example, the so-called glassine or greaseproof papers, or ordinary thin paper stock.

The systems specifically described in this application are highly heatand light-sensitive requiring, for exarnple, exposure to teat sources of the order of C. for only very short time periods. These temperatures and exposure times are the same as or appreciably lower than those commonly required in the diazo reproduction processes now known in the art.

The coated papers of the invention are easily adaptable to use in machines now commercially available for thermal reproduction processes such as the so-called Therrnofax process. Similarly, the ultraviolet sources used for bleaching exposures can be those now employed in commercial diazotype processes, such as in the Ozamatic machine.

To inhibit absorption of the heatand light-sensitive compositions of the invention into a porous substrate such as of paper, it is preferred, but not necessary, to first apply an undercoating layer to the paper. The use of a synthetic or natural resinous substance, for example polyvinyl acetate, or of any other water-resistant chemically inert material as an undercoating layer will inhibit ab sorption of the coating materials by the substrate, and will keep the heatand light-sensitive chemicals at the surface of the substrate. Depending on the initial absorbance of the materials to be coated, under-coating materials may be applied in amounts of anywhere from /2 to 2 lbs. per 3090 sq. feet.

The thermal and light-sensitive coating is generally applied to a carrier in thickness such that /2 to 1 /2 lbs. of dry solids are present per 3000 sq. feet of coated substratc. However, larger or smaller amounts may be employed depending on the color density and sensitivity required in the coating, and the active materials may be combined with an inert resinous binder, if desired.

Finally, to improve the moisture resistance and storability of the sensitive coated material just described, it may be desirable to apply a thin moisture-resistant barrier overcoating atop the sensitive layer. Such coatings may, for example, comprise materials such as paraffin or natural or synthetic resinous materials such as polyvinylidene chloride applied in amounts of from /2 to 4 lbs. per 3000 sq. feet of substrate. The coating layers are suitably applied with the coating substances in solution in an inert solvent whose nature is not otherwise critical. For the diazo layer, solvents such as methanol, ethanol, acetone, methyl ethyl ketone and other such volatile polar organic materials have proved to be good solvents for the diazo compounds and couplers involved. As mentioned earlier, in systems which contain orthodihydroxy couplers, the presence of borax is particularly useful in stabilizing the systems against changes due to aging at room temperature and/or under conditions of high humidity. The presence of borax is optional, but particularly good results in stabilization have been obtained when the molar ratio of borax to coupling agent varies between about 1:10 and about 1:30. However, there is nothing critical about these ratios, and larger and smaller quantities can be employed to achieve speciiically desired degrees of stability in particular cases.

It has heretofore been observed in the art, and is also true of the present system, that improved results in diazotype systems are observed in the presence of organic acid materials. Conventionally, a material such as citric acid or an equivalent, preferably solid, weak organic or inorganic acid is included in diazotype systems. Though such materials are not critically present, their presence in the system improves its behavior. The effect of an acidic material in the system is not known, although it has been speculated that the acid plays a buffering role. Since diazo systems of this type are generally non-aqueous systems, the acids present are very little ionized and it is not possible to speak of the pH of the system. When present, however, the acids are usually employed in amounts such that dilution of the system with water results in an aqueous solution having a pH of between about 3.5 and 4.5. Acids such as lactic, stearic, acetic, ascorbic, oxalic, glycollic, malonic, boric, etc. can be used alone, or in combination with each other or with citric acid.

For unknown reasons, the presence of zinc chloride in the compositions of the invention also gives improved results. possibly because of interactions between the zinc chloride and the diazonium cation present in equilibrium in the systems of the invention.

A better understanding of the invention and of its many advantages can be had by referring to the following specific examples given by way of illustration.

EXAMPLE 1 A preferred coating composition was prepared by dissolving the following ingredients in a mixture of 5.0 ml. of water and 95 ml. of methanol:

, Grams 2-methyl-4-diethylaminobenzene diazo sodium sul- An infrared transparent commercially available paper (Riegel GP 22 X8) was coated on one side directly with the solution mentioned above and was air dried.

The coated paper was used in a reflex process by placing the coated paper with the coated side up atop the original to be copied, the original being face up. The two sheets were passed through a Thermofax Secretary machine. Infrared radiation passing through the copy paper was absorbed by the image areas of the original, converted to heat, and conducted back to the copy paper. The heat promoted coupling and dye formation in the copy paper over the image areas of the original. The copy paper was then exposed to ultraviolet light in a Ozalid machine for a few seconds to produce a fixed copy of the original image, resistant to further light or heat, on a colorless background.

Another sheet of the copy paper was exposed to an ultraviolet source, coated side up, through a translucent original to be copied. Where light penetrated the original, i.e., in the non-image areas, decomposition of the active ingredients of the copy sheet coating occurred. After exposure to ultraviolet, the copy sheet was then heated for a short period during which coupling and dye formation between the diazonium compounds and the coupler occurred in the areas not exposed to and bleached by the ultraviolet light source.

A copy paper of improved stability was prepared by pre-coating an infrared transparent paper of the type earlier described, prior to sensitization of the copy paper, with a water-resistant coating containing 0.4% by weight of borax. The pre-coat inhibited soaking in of the sensitive layer into the paper substrate, and the presence of the borax in the pre-coat lends additional moisture stability to the paper when subsequently coated with the heatand light-sensitive composition.

Still further samples were prepared in which paratfin overcoats were applied to sensitized papers and to precoated sensitized papers.

6 EXAMPLE 2 A coating composition was prepared by dissolving the following components in a mixture of 37.0 gms. water and 55.0 gins. methyl alcohol:

Grams 2,5diethoxy4-morpholinobenzene diazo sodium sulfonate 2,3-dihydroxynaphthalene 2,5-diethoxy-4-morpholinobenzene diazonium chloride zinc chloride salt 0.70

The material was used to coat commercially available papers for the preparation of copy media suitable for use in the reflex and heat developable diazo processes.

Improved stability of papers coated with the above composition was observed upon addition of 0.23 gms. of sodium borate and 0.20 gms. of citric acid to the coating composition described above.

EXAMPLE 3 Heat and light-sensitive compositions suitable for the preparation of coated printing media for data reproduction were prepared by dissolving the following ingredients in 5 gms. of water and gms. of methyl alcohol:

Grams 2-rnethyl-4-diethylaminobenzene diazo sodium sulfonate 2.0 2,3-dihydroxynaphthalene 3.5 4-diethylaminobenzene diazonium chloride zinc chloride salt 0.75 Citric acid 0.3 Sodium borate 0.5

The compositions were used for the preparation of coated data reproduction media, including coated papers having either or both water-resistant precoats and waterresistant overcoatings.

EXAMPLE 4 A non-aqueous .heatand light-sensitive composition was prepared by dissolving the following ingredients in 95 gms. of methyl alcohol:

Flexible substrates were coated with the composition to prepare media suitable for data reproduction processes of the type described herein.

EXAMPLE 5 A heatand light-sensitive coating composition was prepared by admixing the following ingredients in 5 gms. of water and 95 gms. of methyl alcohol:

Grams 4-diethylaminobenzene diazo sodium sulfonate 2.0 2,3-dihydroxynaphthalene 3.5

4-diethylaminobenzene diazonium chloride zinc chloride salt 0.8 Zinc chloride 0.5 Sodium borate 0.5 Citric acid 0.3 The composition were used in the preparation of coated data reproduction media of the type described earlier herein.

Although specific embodiments have been shown and described herein, it will be understood that they are illustrative and are not to be construed as limiting on the scope and spirit of the invention as defined in the appended claims.

What is claimed is:

1. In a data reproduction process for producing a pos itive copy of an original having image areas and nonimage areas in a copy medium comprising a heatand light-sensitive composition and a carrier therefor, said composition comprising a diazosulfona-te salt and a coupling agent reactive therewith under the influence of heat, which process comprises exposing said copy medium to heat in those of its portions corresponding with image areas of the original, whereby color is formed in the heat struck portions of said copy medium by reaction of said diazosulfonate salt and said coupling agent, and densensitizing said copy medium in those of its portions corresponding with non-image areas of the original by exposing said medium to ultraviolet light, whereby said diazosulfonate salt is decomposed and rendered incapable of reaction with said coupling agent, the improvement of further adding to said composition a diazonium salt supplying a diazonium cation to said composition.

2. In a data reproduction process for producing a positive copy of an original having image areas and nonirnage areas in a copy medium comprising a heatand light-sensitive composition and a carrier therefor, said composition comprising a diazosultonate salt and a coup'iing agent reactive therewith under the influence of heat, which process comprises transferring heat from image areas of the original to portions of said copy medium corresponding with image areas of the original whereby color is formed in heat struck portions of said copy medium by reaction of said diazosulfonate salt and said coupling agent, and then desensitizing said copy medium in those of its portions corresponding with non-image areas of the original by exposing said medium to ultravioiet light, whereby said diazosulfonate salt is decomposed and rendered incapable of reaction with said coupling agent, the improvement of further adding to said composition a diazonium salt supplying a diazonium cation to said composition.

3. In a data reproduction process for producing a positive copy of an original having image areas and nonimage areas in a copy medium comprising heatand light-sensitive composition and a carrier therefor, said composition comprising a diazosulfonate salt and a coupling agent reactive therewith under the influence of heat, which process comprises exposing said copy medium to ultraviolet light through said original, whereby portions of said medium corresponding with non-image areas of the original are desensitized by decomposition of said diazosulfonate salt which is rendered incapable of reaction with said coupling agent, and then heating said copy medium to form color by reaction of said diazosulfonate salt and coupling agent in those unexposed areas of said medium corresponding with image areas of the originai, the improvement of including in said composition a diazonium salt supplying a diazonium cation to said composition.

A process as in claim 1 wherein said composition is coated on a substrate.

2 wherein said diazosulfonate and said cliazonium cation has the formula R'NEN+ where R and R are aromatic groups and X is an alkali metal ion.

7. A process as in claim 3 wherein said diaosulfonate salt has the formula RN=NSO X and said diazonium cation has the formula R'NEN where R and R are aromatic groups and X is an alkali metal ion.

8. Heatand light-sensitive compositions comprising a diazosulfonate salt, a coupling agent reactive with said diazosulfonate salt under the influence of heat to form color, and a further diazo material which is a diazonium salt supplying a diazonium cation to said composition, said diazosulfonate salt being decomposable by irradiation with ultraviolet light to render it incapable of reaction with said coupling agent.

9. A heatand light-sensitive copy medium for data reproduction processes comprising a substrate coated with a heatand light-sensitive composition comprising a diazosuifonate salt, a coupling agent reactive with said diazosulfonate salt under the influence of heat to form color, and a further diazo material which is a diazonium salt supplying diazonium cation to said composition, said diazosulfonate salt being decomposable by irradition with ultraviolet light to render it incapable of reaction with said coupling agent.

10. A copy medium as in claim 9 wherein said substrate is paper.

11. A copy medium as in claim 9 wherein said substrate is paper transparent to infrared radiation.

12. A copy medium as in claim 9 wherein said diazosulfonate salt has the formula RN=NSO X and said diazonium cation has the formula R'NEN' where R and R are aromatic groups and X is an alkali metal ion.

13. A copy medium as in claim 12 wherein R and R are the same aroma-tic group.

References Cited by the Examiner UNITED STATES PATENTS 1,934,011 11/1933 Schmidt et al. 96-75 X 2,217,189 10/1940 Sus 96-91 X 2,500,099 3/1950 Straley 96-91 2,659,672 11/1963 Leuch 96-49 2,680,062 6/1954 Sus 96-91 X 2,694,009 11/1954 Sus 96-49 X 2,732,299 1/1956 Morrison 96-49 2,774,669 12/1956 Marron et al. 96-49 3,113,865 12/1963 Sagura et al 96-49 3,153,592 10/1964 Klimkowski et al. 96-91 X OTHER REFERENCES Kosar, Jarmir, Light Sensitive Systems, N.Y., John Wiley & Sons, 1965. TR35 0A5 (pp. 269270).

NORMAN G. TORCHIN, Examiner. C. L. BOWERS, R. L. STONE, Assistant Examiners. 

1. IN A DATA REPRODUCTION PROCESS FOR PRODUCING A POSITIVE COPY OF AN ORIGINAL HAVING IMAGE AREAS AND NONIMAGE AREAS IN A COPY MEDIUM COMPRISING A HEAT- AND LIGHT-SENSITIVE COMPOSITION AND A CARRIER THEREFOR, SAID COMPOSITION COMPRISING A DIAZOLSULFONATE SALT AND A COUPLING AGENT REACTIVE THEREWITH UNDER THE INFLUENCE OF HEAT, WHICH PROCESS COMPRISES EXPOSING SAID COPY MEDIUM TO HEAT IN THOSE OF ITS PORTIONS CORRESPONDING WITH IMAGE AREAS OF THE ORIGINAL, WHEREBY COLOR IS FORMED IN THE HEAT STRUCK PORTIONS OF SAID COPY MEDIUM BY REACTION OF SAID DIAZOLSULFONATE SALT AND SAID COUPLING AGENT, AND DENSENTITIZING SAID COPY MEDIUM IN THOSE OF ITS PORTIONS CORRESPONDING WITH NON-IMAGE AREAS OF OF THE ORIGINAL BY EXPOSING SAID MEDIUM TO ULTRAVIOLET LIGHT, WHEREBY SID DIAZOSULFONATE SALT IS DECOMPOSED AND RENDERED INCAPABLE OF REACTION WITH SAID COUPLING AGENT, THE IMPROVEMENT OF FURTHER ADDING TO SAID COMPOSITION A DIAZONIUM SALT SUPPLYING A DIAZONIUM CATION TO SAID COMPOSITION.
 3. IN A DATA REPRODUCTION PROCESS FOR PRODUCING A POSSITIVE COPY OF AN ORIGINAL HAVING IMAGE AREAS AND NONIMAGE AREAS IN A COPY MEDIUM COMPRISING HEAT- AND LIGHT-SENSITIVE COMPOSITION AND A CARRRIER THEREFOR, SAID COMPOSITION COMPRISING A DIAZOLSULFONATE SALT AND A COUPLING AGENT REACTIVE THEREWITH UNDER THE INFLUENCE OF HEAT, WHICH PROCESS COMPRISES EXPOSING SAID COPY MEDIUM TO ULTRAVIOLET LIGHT THROUGH SAID ORIGINAL, WHEREBY PORTIONS OF SAID MEDIUM CORRESPONDING WITH NON-IMAGE AREAS OF THE ORIGINAL ARE DESENSITIZED BY DECOMPOSITION OF SAID DEAZOLSULFONATE SALT WHICH IS RENDERED NCAPABLE OF REACTION WITH SAID COUPLING AGENT, AND THEN HEATING SAID COPY MEDIUM TO FORM COLOR BY REACTION OF SAID DIAZOLSULFONATE SALT AND COUPLING AGENT IN THOSE UNEXPOSED AREAS OF SAID MEDIUM CORRESPONDING WITH IMAGE AREAS OF THE ORIGINAL, THE IMPROVEMENT OF INCLUDING IN SAID COMPOSITION A DIAZONIUM SALT SUPPLYING A DIAZONIUM CATION TO SAID COMPOSITION. 